This invention relates to aluminum base alloys, and more particularly, to improved lithium containing aluminum base alloys.
The aircraft industry has recognized that one of the most effective ways to reduce the weight of an aircraft is to reduce the density of the aluminum alloys used in the aircraft. To accomplish such, lithium has been added to the alloys. However, the addition of lithium has not been without problems. For example, lithium often results in a decrease in ductility and fracture toughness which can make the alloy unsuitable for certain aircraft applications.
The aircraft industry has also recognized that both high strength and high fracture toughness are quite difficult to achieve even in conventional aircraft alloys such as AA (aluminum Association) 2024-T3X and 7050-TX. For example, a paper by J. T. Staley entitled "Microstructure and Toughness of High-Strength Aluminum Alloys", Properties Related to Fracture Toughness, ASTM STP605, American Society for Testing and Materials, 1976, pp. 71-103, reports generally that toughness decreases as strength increases in AA 2024 sheet and AA 7050 plate. Accordingly, it would be desirable if both strength and fracture toughness could be improved in aircraft alloys, particularly in the lighter aluminum-lithium alloys having density reductions of 5 to 15%. Such alloys would find widespread use in the aerospace industry where low weight, high strength and toughness would provide significant fuel savings.